1. Field of the Invention
The present invention relates to a diagnostic sampling device and system for analyzing body fluids and, more particularly, to a diagnostic sampling device and system for testing the pH of feeding tube aspirates.
2. Discussion of the Prior Art
Enteral feeding tubes inserted through the nasal cavity and guided via the nasopharynx and esophagus into either the stomach or small intestine are used to administer nutrients and medication to patients unable to be fed by mouth. Such tubes are typically about 20 to 55 inches long with a perforated distal end or tip for positioning within the body and one or more ports located outside the body at a proximal end of the tube for administering nutrients and medication and aspirating body fluids.
To insure proper placement of an enteral feeding tube, medical personnel must be able to determine the location of the tip of the tube in the body. For example, while some patients may safely receive feedings in the stomach, others may need feedings in the distal duodenum or proximal jejunum; and, accordingly, medical personnel must be able to differentiate between gastric and intestinal feeding tube placement. Medical personnel must also be able to differentiate between gastric and respiratory placement of the feeding tube, since failure to detect respiratory placement of the tube prior to administering nutrients can be fatal.
Feeding tube placement within the body is often confirmed using radiologic or x-ray techniques requiring radiopaque materials such as barium sulfate to be used in forming the enteral feeding tube. Markings on the tube can also be used as a reference when determining the length of the tube inserted. However, when used alone, tube markings provide only a rough approximation of the actual location of the tip of the tube and, since feeding tube placement is typically confirmed at the time of initial insertion and before each intermittent feeding, the practice of using x-rays to locate the tip of the tube can increase the risk of harm to the patient from repeated exposure to x-rays as well as the overall cost of treating the patient.
Other methods of confirming tube position within the body, such as the auscultatory method, are largely ineffective in differentiating between gastric and intestinal location and in ruling out accidental tube placement in the lung.
Recent studies suggest that pH testing of aspirates from enteral feeding tubes can reduce the need for x-ray confirmation of tube placement. See, e.g., Metheny et al, "pH Testing of Feeding-Tube Aspirates to Determine Placement," Nutrition in Clinical Practice, 9:185-190 (October 1994). In addition, intermittent pH testing of feeding tube aspirates can assist in monitoring the effectiveness of certain therapies, thereby providing useful information that can be used by medical personnel to adjust the therapies accordingly.
Currently, pH testing of feeding tube aspirates is accomplished using a syringe to draw fluid directly from the open proximal end of the enteral feeding tube, after which the fluid is deposited onto a chemical strip, such as litmus, for analysis. A disadvantage of this method is that the body fluids are tested in the open and not contained, thereby increasing the risk of contaminating the sample and exposing medical personnel to infectious diseases.
Some of these problems can be avoided by testing the pH of body fluids in vivo using an enteral feeding tube with an integral pH electrode at the tip of the tube and a separate readout module or monitor. A disadvantage of such enteral feeding tubes, however, is that they do not provide direct visual observation of the body fluids being tested so that it is difficult to differentiate between mucosal and pooled gastric-intestinal body fluids. Also, the cost of such enteral feeding tubes and monitors is high when compared to standard enteral feeding tubes, and the tubes must continually be calibrated with the monitors requiring greater technical skill and increasing the likelihood of error.